It does lack counterplay.
There is counterplay though, you can buy QSS and cleanse it. Illaoi can R as he ults to counter his, so can Camille, and maybe Ekko (haven't tested myself tbph, my friend who is an Ekko jungle main says it works though) Fiora can with her W, you can use
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to block the cast after he starts but before it takes affect. Additionally, if he happens to ult a Shaco, Neeko, or LB clone, or Wukong's Decoy his ult goes on cooldown and fails to activate. Also, as for spell shields, Morgana's E isn't broken by the slow, and blocks the ult. Any unstoppable frames can block it, as its a CC effect, so Sion ult, Kled Ult, Mal ult, Olaf ult, GP W, Rengar W, Ornn W, and incidentally, many of his counters top lane are in that list. Any CC cleanse ability can also end it once its active at any point, these include Alistar Ult, QSS, Olaf ult, Rengar W, and GP W-- of which only Ali's ult is new, but I thought it worth mentioning.
It may or may not be adequate, and he may or may not be too strong right now. Those are not things I'm addressing. I'm merely hoping to share some of the honest to god counterplay that the ability certainly does have, despite people's misconceptions.